1. Field of the Invention
The present invention relates to a voltage control apparatus suitable for use in a vehicle AC generator.
2. Description of Related Art
Recently, vehicle electronic device is increased and portable phone becomes popular, so that electric wave noise generated from these devices is increased in both frequency band and electric field strength. A voltage control apparatus for controlling an output voltage of a vehicle AC generator tends to be influenced by the electric wave noise.
Meanwhile, in a recent voltage control apparatus, electric power consumption of IC chips installed therein is reduced, and circuit pattern in the IC chip is fined for increasing a circuit density, so that electric current flowing through the circuit is decreased and impedance is increased. Thus, due to an electric wave noise intruding from the outside, induced voltage tends to arise in the circuit, thereby causing a malfunction of the IC chip. Further, a lead wire connecting the IC chip in the voltage control apparatus with an outside connecting terminal is fined, so that the impedance thereof is increased. Thus, due to the electric wave noise intruding from the outside, induced voltage tends to arise in the lead wire, thereby causing the malfunction of the IC chip.
For preventing the malfunction of the IC chip caused by the electric wave noise, JP-A-64-37043 discloses that entire IC chip and entire lead wire connecting the IC chip with the outside connecting terminal are covered by metal casing. Since the metal casing shields the IC chip and the lead wire from the electric wave noise intruding from the outside, circuit inside the IC chip and the lead wire extending to the outside connecting terminal are prevented from generating the induced voltage.
However, in the conventional method that the metal casing prevents an intrusion of the electric wave noise, a particular metal casing has to be prepared for shielding the electric wave noise, thereby increasing parts cost. Further, additional assembling process is necessary to attach the metal casing after wiring the IC chip and around it, thereby increasing assembling cost.
An object of the present invention is to provide a voltage control apparatus for vehicle AC generator in which an intrusion of an electric wave noise is prevented with low cost.
According to a first aspect of the present invention, an IC chip is attached to a first metal plate, and a lead wire connects the IC chip with an outside connecting terminal. A second metal plate is disposed and has a size to cover the IC chip, and the second metal plate is formed integrally with a negative side wiring for supplying a battery voltage into the IC chip. Thus, during a process of manufacturing the IC chip, an electric wave noise with respect to the IC chip is removed by only attaching the second metal plate to the outside connecting terminal. As a result, parts cost and assembling cost are reduced in comparison with that an additional metal casing is attached thereto after the IC chip is completely made. The first and second metal plates shield the IC chip from the electric wave noise intruding from the outside, so that an induced voltage caused by the electric wave noise hardly arises in a circuit within the IC chip, thereby attaining a voltage control apparatus of which electric wave noise-proof characteristic is improved.
According to a second aspect of the present invention, a position and a size of the second metal plate are set such that the IC chip is encompassed within a projected area of the second metal plate on the first metal plate. By this, the electric wave noise is prevented from intruding into the circuit within the IC chip.
According to a third aspect of the present invention, a position and a size of the second metal plate are set such that both the IC chip and the lead wire are encompassed within a projected area of the second metal plate on the first metal plate. By this, the electric wave noise-proof characteristic is further improved.
According to a fourth aspect of the present invention, the IC chip is formed in a quadrangle, and a distance between the second metal plate and the IC chip is substantially less than 1.5 times of a diagonal length of the IC chip. The induced noise caused by the electric wave noise bypasses through electrostatic capacitance arising between the IC chip or the lead wire and the second metal plate. Thus, the electric wave noise-proof characteristic is further improved.